The field of the invention is that of fabricating integrated circuits using copper interconnect and low-k dielectric for the back end, in particular circuits having Tungsten or other refractory metal contacts that are mechanically and electrically connected to copper lines.
In the course of developing a process for replacing aluminum with copper in the back end of integrated circuits, workers in the field soon realized that it was necessary to line or enclose the copper to prevent it from diffusing or otherwise escaping and reacting with the dielectric and/or having contaminants react with it.
Various liners were tried out, and the strengths and weaknesses of different combinations became known. One such combination that has been generally satisfactory is TaN/Ta.
In the particular case of a low-k interlayer dielectric, however, the process of forming trenches and vias to hold copper interconnect in Damascene style geometries, causes carbon to be released (e.g. by sputtering) from the dielectric material and be deposited over exposed surfaces of the lower conductor. The carbon is a significant contributor to open circuits at the interface between two levels of interconnect, especially between a W contact and copper at the next level.
It has been found that Ti has the property of gettering carbon very efficiently, and also gettering oxygen and nitrogen. Unfortunately, as those skilled in the art are aware, Ti reacts with Cu to form a compound having a high resistance. Therefore, those skilled in the art do not consider Ti to be a suitable material to line Cu interconnect.
Additionally, as dimensions shrink, it becomes important that the liner be thin. If the liner is too thick, the Cu will be too narrow and have too high a resistance. Every additional layer in the liner decreases the amount of copper and therefore increases the resistance of the interconnect.
Thus, those skilled in the art have not been able to solve the problem of providing a liner for Cu interconnect embedded in a low-k dielectric. The solution used for oxide dielectricxe2x80x94Ta/TaNxe2x80x94is not suitable.
The invention relates to a liner for Cu interconnect making contact with a lower level refractory material embedded in low-k dielectric having carbon as a constituent.
A feature of the invention is the use of a Ti lower layer covered with a TiN upper layer.
Another feature of the invention is a triple layer of Ti/CVD-TiN/Ta.